FIGURE 4-8 Dose–response relationship between calcium intake and retention.

SOURCES: Abrams et al. (1999); Ames et al. (1999).

ages of 9 and 18 years as shown in Table 4-14. The differences between girls and boys and between the 9- to 13-year and the 14- to 18-year age groups are small, but statistically significant. The data provide a basis for estimating intake levels needed for this age group relative to bone accretion.

Although it would be expected that bone maintenance is characteristic of young adults overall, there is some evidence of a small accretion of bone mass for persons in their 20s. The magnitude of this reported accretion varies. Specifically, Recker et al. (1992) followed 156 college-age women for 5 years and reported an increase of 12.4 percent per decade (about 1.24 percent per year) in whole-body BMC, but there were smaller increases in clinically relevant sites such as the forearm (4.8 percent per decade or 0.48 percent per year) and the lumbar spine (5.9 percent per decade or 0.59 percent per year). Further, the rate of increase declined each year for this group. The variance was also large in this study, which may be due to the method selected to assess BMC. Barger-Lux et al. (2005) more recently reported an accretion rate of 0.28 percent per year for women in the 20-